Drop generator die processing

ABSTRACT

Processing a die that has an edge and a substrate upon which a layer of moisture permeable material is disposed. The moisture permeable material extends to the edge of the die. One embodiment comprises interrupting the layer of moisture permeable material to form a gap at a boundary near the edge, thereby to substantially block movement of moisture through the gap of the moisture permeable material.

TECHNICAL FIELD

[0001] This invention relates to the production of wafer dies that areeventually used as drop generators in devices such as thermal inkjetprintheads, and to a way of processing the dies to reduce the likelihoodof delamination of thin film layers on the dies.

BACKGROUND OF THE INVENTION

[0002] Drop generators, such as used with inkjet printers for ejectingdroplets of ink, are generally formed over an insulated, rigid substrateto define a printhead. The substrate is often part of a conventionalsilicon wafer that is delineated into an array of individual dies. Eachdie on the wafer is processed to produce a single printhead. The waferprinthead dies are thereafter separated and incorporated into printcartridges or carriers that connect the printhead with an ink supply.

[0003] The printheads are manufactured from selected combinations ofthin film layers of material that are deposited or grown on thesubstrate using processes often adapted from conventional semiconductorcomponent fabrication. In particular, drop generators and associatedcontrol circuitry of the printhead are incorporated into and carried onthe front surface of the rigid substrate mentioned above. In certaindesigns, the material comprising at least one of the thin film layersmay be permeable to moisture. If portions of such layers are exposed tomoisture (such as may occur when the printhead is mounted to the printcartridge), it is possible for the printhead layers to delaminate as theabsorbed moisture penetrates and degrades the moisture permeable layer.

BRIEF DESCRIPTION OF DRAWINGS

[0004]FIG. 1 is a diagram representing a cross section of part of a diethat is processed in a manner consistent with an embodiment of thepresent invention.

[0005]FIG. 2 is another diagram representing a top view of some dies ofa wafer, which dies are processed in accord with an embodiment of thepresent invention.

[0006] FIGS. 3A-3F are detailed diagrams illustrating one preferredmethod of processing a die in accordance with an embodiment of thepresent invention.

[0007]FIG. 4 is a diagram illustrating an alternative application of thepresent invention in a part of a die that carries a fusible link.

DETAILED DESCRIPTION OF EMBODIMENTS

[0008] Reference is made first to FIG. 1, which diagrammaticallyillustrates the primary components of concern in describing a preferredembodiment of the present invention. Specifically, the diagram shows across section taken at the junction of two adjacent dies 22, 24 that arepart of an array of dies on a wafer 20. The dies are depicted in theirorientation prior to being separated by conventional techniques, such asby sawing of the wafer.

[0009] In a preferred embodiment, each die 22, 24 will eventually beused as an inkjet printhead. Thus, each die carries layers of material,in addition to those shown, that are adapted for moving and chamberingink in the printhead, and for controlled ejections of drops from the inkchamber. These layers, which are generally applied using thin filmtechniques, include mechanisms for controlling the firing of theresistor that expels the ink drops. Such mechanisms include transistorsand associated conductors between the printhead and a controller that isnormally carried in the printer. Where pertinent to the presentinvention, certain of these additional layers are discussed below,primarily in connection with FIGS. 3A-3F. The reader may, however, referto additional U.S. patents for more information about such printheadconstruction. Two of these patents are U.S. Pat. Nos. 6,336,714 and5,635,966.

[0010] Before continuing with this description, it is pointed out thatFIG. 1 shows only a small portion of the wafer and two adjacent dies 22,24, including two, substantially parallel adjacent edges 30, 32 of therespective dies 22, 24. In this embodiment, the space between the twoedges is removed by conventional wafer sawing techniques to physicallydefine the respective die edges 30, 32 after the die fabrication stepsare complete. (Other conventional techniques may be employed forseparating the dies from the wafer.) This space aligns with what isdesignated as a saw street on the wafer prior to separation of the dies.As noted above, for the purposes of explaining this embodiment of theinvention, only the die layers adjacent to the edges 30, 32 arediscussed in this portion of the description.

[0011] In the embodiment shown the wafer 20 generally comprises asilicon substrate 26 upon which is grown a thin silicon oxide 28. Alayer of phosphosilicate glass (PSG) 40 covers the oxide on thesubstrate in the vicinity of the die edges 30, 32 such that, prior toseparation of the dies, the layer of PSG 40 extends from one die to thenext, across the saw street.

[0012]FIG. 1 illustrates the adjacent dies 22, 24 with the layers thatpass through the saw street shown in horizontal dotted lines thatrepresent the position of those layers before the dies are sawn apart.The PSG layer 40 is characteristically moisture permeable. As a result,the edge 40E of that layer that is exposed after the dies 22, 24 aresawn apart is susceptible to the penetration of ambient moisture, whichpenetration is illustrated in FIG. 1 by the wavy arrow 45. The moisturemay originate in the ambient air or, in instances where the die is usedas a printhead, in the liquid ink or vapor that is in the vicinity ofthe edge 40E.

[0013] In one embodiment, the movement of moisture into a die can havethe deleterious effect of disintegrating the PSG layer 40, leading to adelamination of other thin film layers on the die. For example,delamination of the die can cause failure of electrical-signal carryinglayers, such as shown as the conductive layer 42 in FIG. 1. As willbecome clear, embodiments of the present invention tend to prevent suchdelamination.

[0014] It is useful to describe next an exemplary way of fabricating thejust-mentioned conductive layer 42, which in FIG. 1 extends through ahole or via 43 in the PSG layer and in the oxide 28 to contact thesubstrate 26. This via 43 is made by patterning a layer of photoresistmaterial that is laid over the PSG layer 40, and thereafter etching thePSG and oxide to form the via 43. The conductive layer 42 is thereafterdeposited over the PSG and into the via 43, and then patterned andetched to the configuration shown in FIG. 1.

[0015] In one embodiment, the uppermost layer of the dies 22, 24, suchas appears near their respective edges 30, 32, can be referred to as aprotective layer 44 comprising, for example, a deposit of passivationmaterial such as SiN covered with SiC.

[0016] In accordance with this embodiment, the present invention, thedies 22, 24 are processed with the goal of interrupting the continuityof the moisture permeable PSG layer 40 near the location where thatlayer may be exposed to moisture, such as the near the edges 30, 32 ofthe dies. The interruption has the effect of blocking movement of themoisture through the PSG layer 40 (or any other moisture permeable layerinterrupted in accord with an embodiment of the present invention).

[0017] In one embodiment, a barrier 50 is provided for interrupting orseparating the PSG layer 40. In this embodiment, the barrier 50 is verynear the exposed edge 30, 32 of each die and, therefore, the path ofmovement of the moisture 45 is very short, and any attendantdelamination of the die near the edge is inconsequential to theoperation of the die components.

[0018] One way of positioning the barrier 50 to interrupt the PSG layer40 is to first remove a portion of the PSG layer at a boundary near theedge of the die. In one approach, this is done by further patterning ofthe photoresist material that is laid over the PSG layer for making thevia 43 mentioned above. The PSG layer 40 is then etched to form a gap 52in that layer (as well as the via), which gap is illustrated in FIG. 1as the space removed from the PSG layer 40. Depending on the propertiesof the selected etchant, the underlying oxide layer 28 may also beremoved as is also illustrated in FIG. 1. Alternatively, therefore, theoxide layer 28 may remain after the gap 52 is etched.

[0019] The gap 52 in the PSG layer is located near the edges 30, 32 ofthe respective dies and, therefore, underlies the protective layer 44.Accordingly, the deposition of the protective layer (which occurs afterthe formation of the gap 52) substantially fills the gap with theprotective material, thus forming the barrier 50.

[0020] It is contemplated that the gap 52 may be located (or the dielayers selected) such that material other than that of the protectivelayer 44 fills the gap 52 to form the barrier 50. For instance, the gap52 may completely or partially underlie a subsequently deposited metallayer. Accordingly, all or some of the barrier 50 may be metal. It willbe appreciated that such barrier material will serve to block moisturemovement. For that matter, any material that forms a solid barrier andis not moisture permeable (that is, material that has no affinity forabsorbing liquid) will suffice for this embodiment.

[0021] The location and size of the barrier 50 may be selected toconform with manufacturing constraints such as mask layout limitations.For example, in a typical inkjet printhead embodiment, the barrier maybe 2 μm wide (as measured, for example, left to right in FIG. 1), butcan also be much narrower or wider.

[0022] Moreover, rather than forming two barriers 50 (that is, one oneach die 22, 24) so that the saw street is bounded by a discrete pair ofparallel barriers, it is contemplated in one embodiment that all of thePSG layer 40 between the two dies (and across the street) could beremoved (as by the patterning and etching steps illustrated in FIGS. 3Band 3C discussed below), thereby providing a single gap within which astrip of barrier material extends continuously from die 22 to die 24 andacross the street.

[0023] Alternatively, the gap 52 in each die may be formed so that one,inner side of the gap (“inner” being the right side of the gap 52 in die24; the left side of the gap of die 22) is on one side of the respectivedie edge, and the other side of the gap resides in the saw street sothat in one embodiment after the dies 22, 24 are separated there is noPSG layer remaining at the edges of the dies 22, 24. This approachcompletely eliminates any path through moisture permeable material atthe edge of the die.

[0024] In one embodiment, the above-mentioned boundary along which thegap 52 is formed should have an innermost part (that is, the part mostdistant from the die edge) that is sufficiently spaced from the sawstreet to ensure that, due to manufacturing tolerances, the actual sawnedge of the die does not reach the layer of PSG 40 that is just insidethe barrier 50. Put another way, the barrier should be adequately spacedfrom the saw street to ensure that the barrier is not inadvertently cutaway when the dies are separated. In one embodiment of a printhead die,this space (shown as dimension 48 in FIG. 1) is about 20/m.

[0025]FIG. 2 diagrams an embodiment of how the barriers on each die arearranged to extend around the periphery of each die 22, 24. That figureshows (at a much smaller scale as compared to that of FIG. 1) the abovedescribed exemplary dies 22, 24, as well as cutaway portions of twoother dies D3 and D4, in a view that illustrates how the barrier 50 isplaced (that is, how the moisture permeable layer 40 is interrupted)along the periphery of three of the illustrated dies 22, D3, D4 of anarray of dies carried on the wafer 20. The barrier illustrated on theperiphery of die 24 in FIG. 2 is configured in a manner somewhatdifferently from that of the other dies on the wafer for illustratinganother way of providing the barrier. The barrier on that die 24 isformed of two discrete segments 51, 55. This embodiment is used in someapplications where it is difficult to form a single continuous barrieraround the entire periphery of the die.

[0026] In this two-segment arrangement, one barrier segment 55 is formedto define a U-shape substantially around all but one side (the top sidein FIG. 2) of the die 24. The other barrier segment 51 is separatelyformed also to define a U-shape (inverted in FIG. 2) aroundsubstantially all but one side of the die (the bottom side in FIG. 2).In this embodiment, the barriers 51, 55, therefore, overlap along theentire length of each opposing side edge of the die. It will beappreciated that in this configuration moisture can move from a sideedge into the die by following a very lengthy path along and between theentire overlapped parts of the barriers 51, 55. In one embodiment, thispath is sufficiently long for preventing moisture from reaching theinterior of the die during the useful life of the die.

[0027] This description now turns to the particulars of how diecomponents of interest here are fabricated in a way to carry out thepresent invention, and reference is made to FIGS. 3A-3F.

[0028]FIG. 3A represents a partial assembly of a die 124 correspondingto an intermediate step in one embodiment of the fabrication process.The die 124 is adapted to include the present invention. Any of a numberof fabrication methods can be followed to arrive at what is shown andnext described with reference to FIGS. 3A-3F. One such process isdescribed in the previously mentioned reference, U.S. Pat. No.5,635,966.

[0029]FIG. 3A shows the front surface 134 of the upper portion of asilicon substrate 130 that is like the substrate 26 described above inconnection with FIG. 1. Only a portion of the thickness of the substrate130 (that is, the upper portion) is depicted in FIGS. 3A-3F.

[0030] The substrate in this embodiment is doped to form a source region138 and drain region 139 of a transistor for controlling an adjacentfiring resistor (not shown) of an inkjet printhead. A gate oxide (GOX)layer 147 is provided for defining the transistor gate dielectric layer.Atop the GOX layer 147 there is deposited and patterned a layer ofpolysilicon 145 to define the gate region of the transistor.

[0031] Away from the transistor region, the oxide layer is grown thickerto provide a field oxide (FOX) layer 128 that provides in a printheadthe electrical and thermal insulation for isolating individualtransistors on the die. In some embodiments, this FOX layer is notrequired.

[0032] The assembly of FIG. 3A also shows a layer of phosphosilicateglass (PSG) 140 that is deposited using, for example, plasma-enhancedchemical vapor deposition (PECVD). The PSG layer 140 can be about 8000 Åthick (the layers not being shown to scale in the figures). Respectiveto the printhead components of the die, the PSG layer 140 serves as adielectric layer for isolating the transistor gate 145, source 138, anddrain 139 on the substrate 130.

[0033] The PSG layer 140 extends over the FOX layer 128, beyond thefuture edge 132 of the die (that is, the edge that is formed after thedie is sawn from the wafer), and across the saw street between adjacentdies and across the future edge of the adjacent die (not shown), as isdescribed above in connection with FIG. 1.

[0034] In accordance with this embodiment, and with reference to FIGS.3B and 3C, the moisture permeable PSG layer 140 is patterned (FIG. 3B)and etched (FIG. 3C) to form the gap 152 in the PSG layer. Thispatterning and etching preferably is done at the same time (and usingthe same photomask to create the photoresist layer 141, FIG. 3B) thatthe PSG layer is patterned and etched to form other components of thedie, such as the vias 143 depicted in FIG. 3C. As noted, these vias 143provide openings where a subsequently deposited metals layer can contactthe transistor source, drain, and gate, as well as the substrate. Theetching of the PSG layer 140 may be carried out using, for example, acombination of CF₄, CHF₃, and Ar.

[0035]FIG. 3D illustrates a layer 142 comprising two metals. The layer142 is deposited over the PSG layer 140, patterned using a photomask,and later etched (as at 151, FIG. 3E) for the purpose of providing theconductive lines to carry power to the above mentioned firing resistor,and establish the width of that resistor. Preferably, the metals 142 aredeposited in sequence using the same metal deposition tool, with onemetal comprising TaAl (about 900 Å thick) and the other comprising AlCu(about 5000 Å thick).

[0036] In one preferred embodiment, the metals layer 142 is etched awayfrom the edge 132 of the die (FIG. 3E) and, therefore, does not formpart of the material that forms the barrier 250. It is contemplated,however, that the metal layers 142 can be retained in the gap 252 and,along with the protective layer 144 described below, form an effectivebarrier 250.

[0037]FIG. 3F illustrates the deposition of a protective layer 144. Thislayer, among other things, covers and protects the printhead resistorsfrom corrosion and other effects that might occur if the resistor wereexposed to ink. The protective material may be made up of a deposit ofSiN (about 2,500 Å) covered with a deposit of SiC (about 1,250 Å). Aconventional PECVD reactor may be employed for this deposition.

[0038] In this embodiment of the invention, the protective layer 144provides the barrier 250 (FIG. 3F) that, as described above, is locatedand sized for interrupting the moisture permeable layer of PSG 140 and,thus, limiting the length of the possible path for moisture to move inthat PSG layer.

[0039] In the embodiment shown in FIG. 3F, the barrier 250 seals the PSGlayer 140 at the gap 252, extending from the substrate 130 through thegap 252, and over the top surface of the PSG layer 140 in the vicinityof the gap. FIG. 3F also shows the edge of the die 124 after its edge132 is sawn from the wafer.

[0040] It is contemplated that the edge of the die may be one other thanthat formed when the die is sawn. For instance, such an edge in asubstrate may be formed by etching the substrate to make a slot or holein the substrate for directing ink therethrough. Such an ink-directingslot is illustrated in dashed lines at 60 of the die 24 of FIG. 2. Theslot 60 is surrounded with an adjacent barrier 53 that apart from itslocation otherwise matches the construction of a peripheral barrier 50as discussed above. Also, openings (such as through substrateinterconnects) may be formed from the back to the front of the substrate(through the oxide layer) to pass conductive traces. Such openings alsohave the potential for exposing part of the moisture permeable materialto ambient moisture and also may be isolated with a barrier in accordwith the present invention. In any event, the method of the presentinvention is applicable in any situation where moisture permeablematerial is exposed, such as may result from any mechanical or chemicalaction in the vicinity of that material.

[0041] It is noteworthy that for dies having a central ink slot (such asappears at 60 in FIG. 2), with the barrier 53, in one embodiment,barriers at the side edges of the dies are also. The side-edge barriersare employed for preventing penetration of ambient moisture into themoisture permeable layer. Also, in a printhead application, the sideedges of these dies may be repetitively brushed with the wipermechanisms of printhead service stations, which can have the effect ofdelivering small amounts of residual ink into direct contact with theedge. Accordingly, using only a single barrier to surround an ink slotin one embodiment does not address the edge delamination problemidentified here.

[0042] It is contemplated that there are many possible ways ofimplementing embodiments of the present invention to limit or preventthe movement of moisture in a moisture permeable layer of material, suchas PSG, in instances where that material may become exposed to moisture.One alternative embodiment of the present invention is illustrated inFIG. 4, which shows a cross sectional diagram of a portion of aprinthead die 224 that carries a fusible link 300. Such links aresometimes used in printhead encoding systems as explained in detail inU.S. Pat. No. 6,325,483.

[0043] Respective to embodiments of the present invention, a fusiblelink 300 is deposited and patterned to reside atop a layer of PSG 240 ina die 224 that may be otherwise constructed in accord with the abovediscussion of the dies 24, 124. The link 300 is covered with aprotective layer 244 similar to the protective layer 144 described abovein this embodiment. One part of the link is in electrical communicationwith a sense line or current source (not shown), such as through contactpad 302. Another part of the link 300 is connected, as by conductor 242,to the encoding circuitry (not shown) on the die 224.

[0044] In one embodiment, the identification aspect of some selectedlinks (such as the link 300 under consideration here) is carried out byapplying sufficient current through the link to destroy the link in amanner akin to blowing a fuse. The physical effect of blowing the link300 is to disintegrate part of the link as well as a portion of theprotective layer 244 that is adjacent to the link. The absence of thismaterial creates a void (shown as dashed lines 304) that exposes aportion 306 of the PSG layer 240 to ambient moisture, which moisture mayinclude a small amount of residual ink in the vicinity of the fuse. Themoisture, if left unchecked, would be absorbed by the moisture permeablePSG layer and penetrate along paths 245 in that layer, thus causingdelamination problems in layers elsewhere in the die, as mentionedabove.

[0045] In accordance with an embodiment of the present invention, theportions of the PSG layer 240 that underlie fusible links 300 areprovided with gaps 252 that are filled with material to form a barrier250. The barrier is formed in substantially the same manner as describedabove in connection with barrier 152 of FIG. 3, including the etching ofthe PSG layer 240 to form the gap 252 that is filled and overlaid withanother layer to form the barrier 250. In this instance, it will beappreciated that some conductive material 242 may be part of thematerial that makes up the barrier 250 as is seen in the rightmost partof barrier 250 in FIG. 4. In any event, the boundary of the barrier 250is established to surround the fusible link 300 so that any moisturepenetrating the PSG layer 240 as a result of a blown fusible link willbe blocked by the barrier from moving outside of the barrier to otherfunctional parts of the die.

[0046] Although the foregoing description has focused on the processingof dies for use in printheads in inkjet printing, it will be appreciatedthat the present invention may also be applied to the production of diesused in drop generators for any of a variety of applications or fluids.Moreover, although the embodiment of a printhead die was described asincorporating a silicon substrate, it is possible that other rigidsubstrates, such as glass, will suffice for supporting the remaininglayers.

[0047] Thus, having here described embodiments of the present invention,the spirit and scope of the invention is not limited to thoseembodiments, but extend to the various modifications and equivalents ofthe invention defined in the appended claims.

1. A method of processing a die that has an edge, the die including asubstrate upon which a layer of moisture permeable material is disposed,wherein the moisture permeable material extends to the edge of the die,the method comprising interrupting the layer of moisture permeablematerial to form a gap at a boundary near the edge, thereby tosubstantially block movement of moisture through the gap of the moisturepermeable material.
 2. The method of claim 1 wherein interrupting thelayer includes: removing some of the moisture permeable material alongthe boundary, thereby to define the gap in the moisture permeablematerial; and depositing a barrier into the gap.
 3. The method of claim2 wherein depositing a barrier includes depositing protective materialinto the gap.
 4. The method of claim 2 wherein depositing a barrierincludes depositing metal into the gap.
 5. The method of claim 2 whereindepositing includes depositing the barrier to cover the moisturepermeable material near the gap.
 6. The method of claim 5 wherein thesubstrate is silicon and wherein depositing includes contacting thesubstrate with the barrier thereby to seal the moisture permeablematerial where the moisture permeable material defines the gap.
 7. Themethod of claim 5 wherein the substrate is silicon that carries an oxidelayer between the silicon and the moisture permeable material andwherein depositing includes contacting the oxide layer on the substratewith the barrier thereby to seal the moisture permeable material wherethe moisture permeable material defines the gap.
 8. The method of claim1 wherein interrupting the layer includes removing a first portion ofthe moisture permeable material at the boundary and simultaneouslyremoving a second portion of the moisture permeable material that isspaced from the first portion.
 9. The method of claim 8 wherein removingand simultaneously removing includes simultaneously patterning andetching of the first and second portions.
 10. The method of claim 9wherein etching the second portion forms an opening in the moisturepermeable material.
 11. The method of claim 1 wherein the edge is wherethe die is separated from a wafer, the method including locating theboundary to extend substantially continuously around the entireperiphery of the die.
 12. The method of claim 11 wherein locating theboundary includes defining two substantially overlapping boundary parts.13. The method of claim 11 wherein the die includes a second edgedefined by a slot, the method including locating the boundary adjacentto and substantially surrounding the slot.
 14. The method of claim 11wherein the die includes a second edge around an opening in the die, themethod including locating the boundary adjacent to and substantiallysurrounding the opening.
 15. The method of claim 1 including extendingthe boundary of the interrupted moisture permeable layer tosubstantially surround a fusible member carried on the substrate.
 16. Adie for a drop generator, comprising: a substrate; a moisture permeablelayer disposed on the substrate to extend to an edge of the die; a meansfor separating the moisture permeable layer to form a gap at a boundarynear the edge thereby to block movement of moisture through the gap ofthe moisture permeable layer of the die.
 17. The die of claim 16 whereinthe means for separating is a barrier that is arranged to extendsubstantially continuously around the entire periphery of the die. 18.The die of claim 16 wherein the moisture permeable layer isphosphosilicate glass.
 19. The die of claim 16 wherein the means forseparating is a barrier that is about 2 μm wide.
 20. The die of claim 16wherein the means for separating is a barrier that is spaced about 20 μmfrom the edge of the die.
 21. The die of claim 16 wherein the substrateis silicon and wherein the means for separating is a barrier that isarranged to contact the substrate and to substantially cover themoisture permeable layer at the boundary.
 22. The die of claim 16wherein the substrate is silicon that carries an oxide layer between thesilicon and the moisture permeable layer and wherein the means forseparating is a barrier that is arranged to contact the substrate and tosubstantially cover the moisture permeable layer at the boundary. 23.The die of claim 16 wherein the means for separating is a barrier thatis arranged to extend around a fusible member that is carried on thesubstrate.
 24. The die of claim 16 including a print cartridge to whichthe die is mounted.
 25. The die of claim 16 wherein the means forseparating includes eliminating the moisture permeable layer at theedge.
 26. A method of processing a die that includes a substrate uponwhich is provided a layer of moisture permeable material that underliesa fusible member, comprising the step of substantially enclosing themoisture permeable layer with a substantially moisture impermeablelayer.
 27. A method of processing two adjacent dies that are separatedby a space on a wafer between respective edges of the dies, the waferincluding a substrate upon which a layer of moisture permeable materialis disposed to extend across the space, the method comprising the stepof forming on each die a barrier that interrupts the moisture permeablematerial to provide on both of the dies a discontinuity in the moisturepermeable material near the respective edges of the dies.
 28. The methodof 27 including forming the barrier to extend across each respective dieedge and into the space.
 29. The method of claim 27 wherein the dies aretwo of an array of dies on a wafer, the method including locating thebarrier to extend substantially continuously around the periphery ofeach of the dies on the wafer.
 30. The method of claim 27 includingseparating the dies at the space and mounting one of the dies to a printcartridge.
 31. A method of limiting the length of a path for moisturethrough a moisture permeable material layer of a die, wherein part ofthe moisture permeable material layer is exposable to moisture, themethod comprising the step of interrupting the moisture permeablematerial layer at a boundary near the exposable part, thereby tointerrupt the path for movement of moisture from the exposable part andthrough the moisture permeable material layer.
 32. The method of claim31 wherein the die includes an edge where the die is separated from awafer, the method including the step of locating the boundary near theedge of the die.
 33. The method of claim 31 wherein the interruptingstep includes removing a portion of the moisture permeable materiallayer at the boundary and replacing the removed portion with barriermaterial other than moisture permeable material.
 34. The method of claim33 including the step of removing a second portion of the moisturepermeable material layer at a time simultaneous with removing of theportion of the moisture permeable material at the boundary.
 35. Themethod of claim 31 wherein interrupting includes etching away some ofthe moisture permeable material layer at the boundary.
 36. The method ofclaim 31 wherein the die includes a fusible link that is carried onphosphosilicate glass and is operable to expose the underlyingphosphosilicate glass, the method comprising the step of locating theboundary to substantially surround the fusible link.